EPA and DHA Enhance CACT Promoter Activity by GABP/NRF2

Carnitine-acylcarnitine translocase (CACT) is a nuclear-encoded mitochondrial carrier that catalyzes the transfer of long-chain fatty acids across the inner mitochondrial membrane for beta-oxidation. In this study, we conducted a structural and functional characterization of the CACT promoter to investigate the molecular mechanism underlying the transcriptional regulation of the CACT gene by n-3 PUFA, EPA and DHA. In hepatic BRL3A cells, EPA and DHA stimulate CACT mRNA and protein expression. Deletion promoter analysis using a luciferase reporter gene assay identified a n-3 PUFA response region extending from -202 to -29 bp. This region did not contain a response element for PPAR alpha, a well-known PUFA-responsive nuclear receptor. Instead, bioinformatic analysis revealed two highly conserved GABP responsive elements within this region. Overexpression of GABP alpha and GABP beta subunits, but not PPAR alpha, increased CACT promoter activity, more remarkably upon treatment with EPA and DHA. ChIP assays showed that n3-PUFA enhanced the binding of GABP alpha to the -202/-29 bp sequence. Furthermore, both EPA and DHA induced nuclear accumulation of GABP alpha. In conclusion, our findings indicate that the upregulation of CACT by n3-PUFA in hepatic cells is independent from PPAR alpha and could be mediated by GABP activation.